The invention lies in the field of combustion plants. The invention relates to a method of operating a combustion plant. It also relates to an apparatus for carrying out the method.
For the combustion of a fossil fuel in a combustion space, efforts are focused on constantly improving the combustion process. A suitable firing control is normally provided to achieve an especially good combustion process with as low an emission of pollutants as possible, in particular, CO and NOx, with an especially high efficiency and, at the same time, with a low volumetric flow of flue gas. In such a firing control, the concentration of at least one reaction product produced in the combustion process is usually determined.
During the combustion of fossil fuel or garbage, fluctuations in the calorific value of the fuel or of the fuel mixture may occur, particularly when the fuel has different origins or the garbage has a heterogeneous composition. These fluctuations adversely effect the pollutant emission. The disadvantages also exist during the industrial combustion of residues, during which solid and liquid, as well as gaseous, fuels are usually burned at the same time. If the temperature distribution and the concentration profile of reaction products arising in the combustion process are known, an improvement in the firing control, and, thus, an improvement in the combustion process with regard to low pollutant emissions, can be achieved.
German Utility Model 197 10 206.9 having the title Method and apparatus for analyzing the combustion and monitoring the flame in a combustion space, describes a method in which the temperature distribution and the concentration distribution of a reaction product (produced in the combustion process) in a flame are determined with an optical system. With such a method, the changes in the concentration distribution of the reaction product to be tested can also be determined locally in the combustion space, particularly in a flame. However, only global effects of the combustion process enter the firing control. Thus, efficiency in the case of locally determined distributions is only limited.
In addition, German Utility Model DE 80 17 259.4 41 discloses a firing plant for the controlled combustion of solid fossil fuels. In the firing plant, a plurality of radiation sensors is assigned to the flame region of each individual burner of the firing plant. Control of the individual burners is made possible with reference to the radiation intensity determined for each individual burner. A disadvantage of the plant is that the radiation intensity of an individual flame is determined by a plurality of radiation sensors respectively recording a line of the flame. To record a section of the flame, the radiation sensors are pivotably disposed. Such a configuration is especially time-intensive and complicated. In particular, for a heterogeneous temperature distribution, which normally characterizes the combustion process of a combustion plant configured as a garbage incineration plant, the resulting different local densities of combustion gases are not taken into account in the firing control. Therefore, the influence of the firing control with regard to an especially low pollutant emission is slight.
It is accordingly an object of the invention to provide a method and apparatus for operating a combustion plant that overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and that sets the combustion process for an especially low pollutant discharge simply and quickly.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of operating a combustion plant having a number of burners, the composition of the fuel mixture of each burner being controlled by at least one setpoint determined with reference to dynamic characteristic quantities characterizing the combustion process. In the method, the setpoint for each individual burner is determined as a function of or independence on its contribution to the total proportion of a reaction product produced in the combustion process, in which case, the contribution of each burner to the reaction product is determined for each burner with reference to the dynamic characteristic quantities and static characteristic quantities characterizing the combustion plant.
The invention is based on the idea that global measured values are not sufficient for an especially simple and quick setting of an especially low pollutant discharge. On the contrary, the individual contribution of each burner should be determined and taken into account in the firing control. The determination of the contribution of an individual burner to the concentration quantity of a reaction product produced in the combustion process, in particular, at the outlet of the combustion space, enables the effect of each individual burner with regard to the total contribution to the pollutant emission to be taken into account. Thus, the combustion behavior of an individual burner and its effect on the combustion process can be optimized.
In accordance with another mode of the invention, the determining step is performed by determining the contribution of each burner to the reaction product using spatial resolution.
The local progress of at least one reaction product to be tested, e.g., of a combustion radical or a flue-gas quantity CO or NOx inside the combustion space, up to the outlet of the combustion space is advantageously calculated for each individual burner. The contribution of the burner or of each burner to the reaction product is expediently determined in a spatially resolved manner. In dependence on the contribution of the relevant burner to the concentration quantity of the reaction product, at least one setpoint for the composition of the fuel mixture of this burner is determined. By tracing the respective contribution to the total proportion of the reaction product to be tested in the combustion space, the entire combustion is homogenized and improved by optimizing the individual burners.
In accordance with a further mode of the invention, at least one of the dynamic and static characteristic quantities is processed with a combustion model of the combustion process.
In an especially advantageous manner, the combustion model simulates the combustion process. The combustion model describes the combustion process with reference to the chemical reaction kinetics with suitable differential formulations. The transport processes are described, for example, with reference to the diffusion, the mass flow, and/or the heat flow. The chemical reactions in the combustion space or in the flame, e.g., the oxidation, are described with reference to elementary reactions taking place during the combustion. The physical couplings between the transport processes or material flows of the individual burners and between components of the combustion space, e.g., heat flow between the burner and the wall of the combustion space, are taken into account in the combustion model by the exchanged heat flow, the convection, and/or the radiation.
In accordance with an added mode of the invention, the processing step is performed by simulating chemical reaction kinetics with the combustion model of the combustion process.
In an expedient development, at least some of the characteristic quantities, in particular the dynamic characteristic quantities, are determined with the aid of measurements. For example, the concentration of the reaction product is reconstructed in a computer-tomographic manner from an emission spectrum recorded in the combustion process. In addition, at least some of the characteristic quantities are advantageously output from a memory as filed characteristic quantities. The individual phases of the combustion process can be simulated with these filed characteristic quantities, in which case, by changes in individual characteristic quantities, e.g., the addition of oxygen for O2 enrichment, the combustion process can be optimized with regard to an especially low pollutant emission.
In accordance with yet another mode of the invention, at least some of the dynamic characteristic quantities are output from a memory as filed characteristic quantities.
Characteristic quantities are fed as input quantities to the combustion model. Preferably used as characteristic quantities of the combustion process are: (1) the value of the concentration of the reaction product to be tested, e.g., of the combustion radical Co or CH in the flame of the selected burner; (2) the fuel quantity or fuel feed of the selected burner; (3) the air feed or fed air quantity of the selected burner; and/or (4) at least one alternating quantity of components that are in heat exchange with this burner, e.g., other burners or the wall of the combustion space. The characteristic quantities characterizing the combustion process are dynamic characteristic quantities that are characterized by the respectively associated instantaneous values for a time domain.
In accordance with yet an added mode of the invention, the static characteristic quantities of the combustion plant include at least one of a number of burners used and at least one geometric quantity of a combustion space.
At least one geometric quantity of the combustion space and/or the number of burners used are preferably used as characteristic quantities of the combustion process. These are also called boiler quantities. The characteristic quantities of the combustion plant are static characteristic quantities that describe the combustion plant with respect to the construction and the geometry.
In accordance with yet an additional mode of the invention, at least one of the static and the dynamic characteristic quantities are processed with a combustion model of the combustion process to form an output quantity characterizing an individual/respective burner.
In order to determine the contribution of the individual burner to the reaction product in the combustion space at a preselected location, the characteristic quantities of the burner to be tested are processed with the combustion model to form an output quantity characterizing the burner, e.g., to form a concentration value of a combustion radical to be tested at the outlet of the combustion plant. The output quantity of the burner is then expediently compared with the weighted average value of the output quantities of the other burners. From the comparison, it is already possible to infer a possible malfunction of the respective burner.
The resulting comparison value is preferably used for forming at least one of the setpoints for the composition of the fuel mixture of the relevant burner. With reference to the comparison of the contribution of the individual burner with the total sum of the contributions of all the burners and the setpoint formed therefrom, the combustion behavior of the relevant burner is homogenized and optimized with regard to the entire combustion in an especially advantageous manner.
With the objects of the invention in view, there is also provided an apparatus for operating a combustion plant having a number of burners. The burners are respectively controlled with at least one setpoint for a composition of a fuel mixture, the at least one setpoint being determined with reference to dynamic characteristic quantities characterizing a combustion process. The apparatus has a setpoint module for determining the setpoint for the composition of the fuel mixture of each individual burner in dependence on its contribution to the total proportion of a reaction product produced in the combustion process. The apparatus also has a combustion analysis module for processing the dynamic characteristic quantities and static characteristic quantities characterizing the combustion plant. The combustion analysis module is connected upstream of the setpoint module in a signal flow direction in order to determine the contribution of each individual burner. The combustion model is expediently stored in the combustion analysis module.
In accordance with again a further feature of the invention, there is provided a data processing module for determining the dynamic characteristic quantities of each burner of the burners. The data processing module is connected to the combustion analysis module for processing the dynamic characteristic quantities. Preferably, the data processing module is connected upstream of the combustion analysis module in a signal flow direction.
In accordance with again an added feature of the invention, the combustion analysis module is two combustion analysis modules and including a data module for filed dynamic characteristic quantities, the data module being connected upstream of at least one of the two combustion analysis modules in a signal flow direction.
In accordance with again an additional feature of the invention, the data module is connected upstream of a second of the two combustion analysis modules in a signal flow direction.
In accordance with still another feature of the invention, the static characteristic quantities fed to the combustion analysis module are expediently stored in a data memory. The combustion behavior of the individual burner or of a combination of a plurality of burners can be simulated in an especially advantageous manner with the characteristic quantities filed in the data module and in the data memory and the resulting flue-gas values. The stored characteristic quantities are varied by small amounts and are processed with the above-described combustion model until a predeterminable flue-gas value or value of the reaction product is set. With reference to the value determined, which, for example, represents an especially low emission of the reaction product, setpoints of the individual burners with regard to the composition of the respective fuel mixture are then set.
To homogenize the combustion behavior of the individual burner, the combustion analysis module is preferably connected to the setpoint module, on one hand, directly and, on the other hand, with an averaging module and/or a weighting module in between. Therefore, a setpoint, determined by the setpoint module, for the composition of the fuel mixture of the relevant burner can be determined in dependence on the other burners participating in the combustion process. The setpoint module can set the combustion behavior of each burner. Therefore, an especially low pollutant emission is achieved by such a specific control of each burner.
In accordance with still a further feature of the invention, the at least one combustion analysis module has a combustion model.
In accordance with a concomitant feature of the invention, there is provided at least one of an averaging module and a weighting module, and the setpoint module is connected to the at least one combustion analysis module with the at least one of the averaging module and the weighting module in between. The averaging is preferably disposed upstream of the weighting module in a signal flow direction.
Advantages achieved with the invention, in particular, include the fact that, by determining the contribution of an individual burner to the total value of a reaction product to be tested, e.g. of a flue-gas quantity, the operating mode of each individual burner can be set to improve the entire combustion with regard to an especially low pollutant emission. A uniform combustion behavior of all the burners is permitted, in particular, by the burner-resolved determination of the respective flue-gas values of all the burners at the outlet of the combustion plant and by the subsequent mutual optimization of the burners. The processing speed for the combustion module is especially high due to the fact that the entire combustion is split up among the individual burners. Therefore, the method together with the apparatus is suitable for controlling a combustion plant in real time.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and apparatus for operating a combustion plant, it is, nevertheless, not intended to be limited to the details shown since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.